Alkylation process



Patented Apr. 26, 1949 2,468,529 ALKYLATION PROCESS Alexis Voorhies, Jr., Baton Rouge, La., and Ashley Sydnor, Jr., Fanwood, N. J.,

Oil Development Company, a corporation of Delaware Standard asslgnors to No Drawing. Application December 13, 1945. Serial No. 634,886

2 Claims. (Cl. 260-6834) This invention relates to a low temperature alkylation process for producing an alkylate of high anti-knock quality and high flash point.

In order to reduce the hazard from fire which is attendant to the crash landing of aircraft, it has been proposed that the customary flammable gasoline used as fuel be replaced by a material which will not readily ignite at atmospheric temperature, yet will perform satisfactorily in an internal combustion engine of the conventional Otto type. The requirements for such a fuel are that it be substantially equal in anti-knock quality and heating value to conventional high octane number aviation gasolines, yet have a flash point high enough so that its vapors will not readily ignite from a spark under atmospheric conditions. A fuel having a Tag closed cup flash point of at least 100 nated as safety fuel.

We have found that by the proper choice of operating conditions and catalyst the alkylation reaction can be controlled so that when low molecular weight isoparafilns and mono-olefins are alkylated, high octane number isoparaffins boiling in the safet fuel range are produced in relatively high concentration. For example, when isobutane is alkylated with butylenes in the presence of concentrated sulfuric acid in the conventional manner at 35 to 50 F. for the production of alkylate boiling in the gasoline range, that portion of the product which has a volatility suitable for inclusion in safety fuel usually comprises less than 10% (vol.) of the total alkylate, and has an ASTM octane number generally not exceeding 86. We have discovered that when isobutane and butylenes are alkylated, using as a catalyst a mixture of sulfuric acid and ethylene or ethyl sulfate at temperatures below 20 an unusually high yield of material boiling above 300 F. and having a flash point above 100 F. is produced. We have also discovered that this material is of superior quality for use as a safety fuel. Thus, when the alkylation temperature was decreased from 38 F. to F., the clear ASTM O. N. of the safety fuel cut increased from 85.2 to 91.1.

F. may be properly desig- In carrying out the alkylation at temperatures F., it is important to use suitable below 20 diluents strength in the sulfuric acid catalyst. The of the sulfuric acid used in the low temperature alkylation is about 96% to 98%, preferably about 98%, and such acid will tend to freeze at temperatures between about +20 F. and +30 F. if its freezing point is not suitably depressed. The suitable diluents prevent the sulfuric acid from freezing at temperatures below +20 F. down to as low as 20 F., while they maintain adequate catalytic activity of the acid and effect some regulation of the reaction not fully understood at present.

We have found that ethylene, ethyl sulfate, dimethyl ether, and similar low boiling aliphatic compounds are suitable diluents for the purpose of maintaining the desired catalytic activity in alkylation at the low temperatures. These suitable diluents are characterized by their tendency to exist in the catalyst composition as aliphatic sulfates, being sulfates initially or forming sulfates when absorbed by the acid. They are further characterized as being substances which do not weaken the acid by formation of substantial amounts of water on admixture with the acid. They contain alkyl groups which are lower in molecular weight than the hydrocarbon reactants.

For example, they may be compounds which acquire the form of methyl, ethyl, or propyl sulfates in the catalyst'for, the alkylation of the C4 isoparaflins with C4 mono-olefins. Accordingly, the lower alcohols, C1 to C3 alkanols, cannot be used except to a very limited extent as diluents, since they have the tendency to form water by reaction with the sulfuric acid.

A minor proportion of diluents is mixed with the sulfuric acid in the catalyst solution, preferably from 0.1 to 0.5 mole per mole of sulfuric acid. By thus limiting the amount of diluent in the catalyst solution, the titratable acidity of the solution can be maintained at a proper concentration above The following tabulated data illustrate typical conditions and results of the low temperature alkylation conducted in accordance with the present invention and make a comparison with conventional higher temperature alkylation treatments.

1 of the acid Allculate safety fuels Feed Stock.. Isobutane-Butyicnes 987 11,804 Catalyst 98% mso. 98% mso. fiiiuent Solution 2 Reactor Temperature 70 38 External lsobutane Olefin Ratio (mole basis) 5/1 5/1 6/1 Spent Acid, Percent titratable Acidit 87. 5 91.2 75 AcidConsumptlon lb.l al. of total al in s t iti 0 re s scziit ul 2.2 0.1

Aviation AIM/M Yield on Total Alkyiate, Vol. Percent 87.0 87.3 67.6 M at F 219 220 225 H at F 235 234 264 F. Y F---- 265 251 343 ASTM 0. N., Clean-.- 92-93 94.1 93.0

Safety Fuel Gut 8 23.2 50- 0 55. l 54. 4 305 314 353 323 336 358 348 358 362 372 384 370 401 433 370 2 2 V 2 98 106 120 81.4 85.2 91. 1 94. 0 98. 2 iso 0.03

, maintained constant at 75% 'l'.'itratahle acidl by the addition of This is equivalent to replacement B5SO4/ gallon alkylate.

was .6

rate of 0.

Containing 0.23 mole ethylene/mole nzsoi.

Whereas there was comparatively little change in the octane number of the low flash point aviation alkylate, the safety fuel cut increased in clear ASTM octane number from 81.4 to 91.1 as the temperature decreased from 70 F. to 0 F. Furthermore, the yield of safety fuel was considerably higher in. the 0 F. operation than it was at higher temperatures (23% vs. 8l0%) Our invention maybe applied in any of the' various types of reaction equipment which are generally employed inthe petroleum industry for producing aviation alkylate. 1 It is desirable only to provide additional equipmentv to dissolve the diluents in the acid, such asa vessel in which to absorb ethylene in the catalyst, additional refrigeration distillation column in which the safety fuel may be fractionated from'the. other components of the total alkylate product;

It will be noted that of the factors which contribute to production of high anti-knock safety fuel compounds in increased amounts, the most important are the lowering of the temperature and the use of the suitable diluents in the catalyst solution. v

The preferred low temperature alkylation re-. action temperature is in the proximity of 0 F., e. g., about 0 to 5 F; With the suitable diluents. which in small amounts depress the freezing point from above F. to below 0 F., the tltratable acidity of the catalyst can be maintained at high levels from 70% to about 98%, the alkylate yield and quality being increased with the'acidity.

examples 1.to'3 carbon atoms components which comprises per cent of isobutylene in the total olefin feed, there is considerably less catalyst degradation and .the quality of the safety fuel cut is substantially improved as compared to a feed in which 15% by volume or less of the olefins is isobutylene. The yield of safety fuel alkylate was shown to be nearly doubled on increasing the volume per cent of isobutylene from 15% to 30% on total olefins 5 to 10% normal butylenes volume of isobutane.

By using the improved low temperature alkylation conditions, in general, safety fuel alkylates boiling in the range of 300 F. to 420 F. with clear octane'numbers above 88 are'obtained in yields amounting to about 20 volumeper cent of total alkylates; whereas under alkylation conditions conventionally used in the past for producing maximum yields of lower boiling alkylates, only about 10% of material boiling in the range of 300 F. to 420 F. was formed, and this material has clear octane numbers of only'80 to 85.

The improved safety fuel products of this process may be used as an base alone, or with other kinds of safety fuel ingredients. They may be used with fuel additives, such as gum inhibitors,

and at least 70% by agents. They are generally to addition of about 2 to 5 cc. of tetraethyl lead per gallon in formulating a satisfactory given for the purpose but is intended come within the spirit and scope, thereof.

We claim: 1. The process of preparing aviation safety fuel solution of sulfuric acid having a strength of about 96% to- 98% with a small proportion of an aliphatic sulfate containing alkyl groups of to depress the freezing point of the acid from above +20 F. to below 0 F., and alkylatinga liquefied normally gaseous isoparaffin with a liquefied normally gaseous olefin at a temperature in the range of -20 F. to +20 F. in the presence of said catalyst fresh sulfuric acid facilities, andasaid catalyst It is of interest to note that low temperature solution. v

2. In an alkylation of isobutane with butylenes, the steps which comprise absorbing into about 98% strength sulfuric acid from 0.1 to 0.5 mole of ethylene per mole of sulfuric acid to form a catalyst solution in w oh the freezing point of the sulfuric acid is lowered from above +20 F. to below 0 F., alkylating isobutane with butylenes including isobutylene in the presence of said catalyst solution, and maintaining the acidity of solution between 70% and 98% while-the solution is maintained liquid at a temperature below +20 F.

ALEXIS VOORHIES, JR. ASHLEY R. SYDNOR, Ja.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,169,809 Morrell Aug. 15, 1939 2,341,487 Taylor et al. 1..- Feb. 8, 1944 2,366,716 Frey Jan. 9, 1945 9,371,408 Parker Mar. 13, 1945 2,381,041 ,De Jong Aug. 7, 1945 in a refinery cut containing aviation safety fuel dyes, color I stabilizers, anti-oxidants, and various anti-knock be used with an aviation fuel. The invention is not to be limited by the specific of illustration: to include modifications which forming a catalyst 

